1. (Field of the Invention)
The present invention generally relates to an X-ray analysis apparatus whose detector part turns or shuttles to accomplish a continuous scanning.
2. (Description of the Prior Art)
In an X-ray fluorescence spectrometer of a wavelength dispersive type currently widely in use, a sample to be analyzed is irradiated by primary X-rays so that fluorescent X-rays are emitted from the sample. The fluorescent X-rays emitted from the sample are monochromated by a spectroscopic device such as an analyzing crystal, and the resultant, spectroscopically analyzed fluorescent X-rays are then detected by a detector which subsequently outputs pulses. Although the voltage of the pulses outputted from the detector, that is, the pulse height value is proportional to the fluorescent X-ray energy and the number of the output pulses per unitary time is proportional to the intensity of the fluorescent X-rays, of those output pulses the output pulses falling within a fixed range of pulse height values are selected by a pulse height analyzer and the number of those selected output pulses is counted by a scaler. In other words, the count of the selected output pulses is determined by a scaler.
In a scanning type of X-ray spectrometer, the spectroscopic device is scanned linked with the detector so that the wavelength of the monochromated X-rays change. One of the mechanism for the linkage is called as goniometer. Specifically where a qualitative analysis or a semi-quanfitative analysis is performed, the fist speed is required and, therefore, the spectroscopic device and the detector are continuously scanned. In other words, the scanning method is not step scan in which the goniometer is driven a predetermined angle and is then halted for a predetermined time during counting of the output pulses, but continuous scanning in which counting of the output pulses is carried out by continuously driving of the goniometer. At this time, for each fixed scanning interval, for example, {fraction (1/100)} degree of the rotation angle of the detector (so-called 2xcex8) the scaler reads the count as an intensity for each scanning interval.
The relationship between the scanning range (2xcex8) of the goniometer and the scanning speed thereof is shown in FIG. 2. In order for the goniometer to be continuously driven at a desired high speed as shown by xe2x80x98bxe2x80x99 in FIG. 2, the goniometer has to be driven with accelerated speed as shown by xe2x80x98axe2x80x99 in FIG. 2 before it is driven to the desired high speed. Also, to halt the goniometer being then driven at the high speed, the goniometer has to be driven with decelerated speed as shown by xe2x80x98cxe2x80x99 in FIG. 2. Accordingly, accurate intensity for each scanning interval can not be obtained in the ranges of accelerated and decelerated speed shown in xe2x80x98axe2x80x99 and xe2x80x98cxe2x80x99, because the time required for each {fraction (1/100)} degree varies.
On the other hand, if a method which counting is not performed in the ranges of the accelerated or decelerated speed shown by xe2x80x98axe2x80x99 or xe2x80x98cxe2x80x99 is taken for accurate measurement, the analyses at each end can not be done. Also, if as shown by the chain double-dashed line counting is performed while the driving speed of the goniometer is lowered to such an extent that neither acceleration or deceleration is not required, an accurate analysis would be possible at both ends of the scanning range, but at the sacrifice of the speed. Accordingly, rapid and accurate measurement of qualitative analysis or semi-quantitative analysis can not be done over a relatively wide range of wavelength.
In addition, in an X-ray diffractometer for analyzing the crystalline structure of sample, in which a sample support to place of the sample to be analyzed and a detector are linked by the goniometer so that the intensity of diffracted X-rays diffracted by the sample can be measured by varying the incident angle of X-rays irradiated upon the sample, a high precision measurement carried out by the step scan requires a relatively long time. On the other hand, the rapid measurement is possible by the continuous scan. However, accurate measurement is not possible because the counting time is not strictly constant for the fixed scanning interval.
While the foregoing description applies where the detector rotates on the spectroscopic device or the sample by the goniometer to accomplish the continuous scan, problems similar to those discussed above can be found even where a measurement unit including an X-ray source and a detector shuttles on a sample by the continuous scan. For example, in a production line in which while a strip of paper is transported in a direction lengthwise thereof a release agent such as silicone is coated on one surface of the strip of paper to form a strip of release coated paper which is subsequently cut longitudinally (in a direction conforming to the direction of transport) for each or sections divided equally in a widthwise direction thereof which is perpendicular to the longitudinal direction (or for each of continuous sections), to thereby provide a plurality of release coated papers, it is required for the purpose of a quality control of the products (i.e., release coated papers) that the amount of silicone coated is determined for each of the sections.
Accordingly, in the conventional X-ray fluorescence spectrometer designed to suit to the particular purpose discussed above, a measurement unit shuttles by a fixed speed on the sample, which is the strip of the release coated paper before being cut into the sections, in a direction widthwise of the strip of the release coated paper generates for unitary time a number of pulses proportional to the intensity of the fluorescent X-ray emitted from silicon as a result of the sample having been irradiated by a primary X-ray while being transported in the direction lengthwise thereof. Of the pulses generated from the measurement unit, the pulses falling within a predetermined pulse height range are selected by a pulse height analyzer and the number of the selected pulses is determined by a scaler. A calculating means for calculating the amount of silicone coated then determines the amount of silicone coated for each section, based on the measured intensity for each section which is obtained by dividing the number of the pulses generated by the measurement unit by the time required for the measurement unit to move a distance corresponding to one section at the fixed speed. It is here assumed that the moving speed of the measurement unit is constant and the time required for the measurement unit to move the distance corresponding to one section is also constant.
However, it has been found difficult to strictly maintain a constant value the speed at which the measurement unit is moved by the drive means, and the moving speed of the measurement unit varies to a certain extent. Consequently, association of the measured intensity with the particular section and, hence, association of the amount of silicon coated with the particular section tends to depart from each other and, therefore the amount of silicone coated cannot be accurately determined for each section.
Accordingly, the present invention is intended to provide an improved X-ray analyzing apparatus of a continuous scanning type in which a detector for detecting the intensity of X-rays is turned or shuttled, which apparatus is effective to achieve a rapid and accurate analysis.
To this end, the present invention provides an X-ray fluorescence spectrometer which includes a sample support of a sample to be analyzed; an X-ray source for irradiating the sample with a primary X-ray to excite the sample to emit a fluorescent X-ray thereform; a spectroscopic device for monocromating the fluorescent X-ray emitted from the sample; a detector adapted to receive the fluorescent X-ray, which has been monochromated by the spectroscopic device, and to generate pulses of a voltage proportional to an energy of the fluorescent X-ray in a number proportional to an intensity of the fluorescent X-ray; and a linkage means for drivingly associating the spectroscopic device and the detector together to allow the sample to be continuously scanned, by causing the monochromated fluorescent X-rays to be incident upon the detector while a wavelength of the fluorescent X-ray monochromated by the spectroscopic device varies.
The X-ray fluorescence spectrometer referred to above also includes a pulse height analyzer for selecting the pulses which fall within a predetermined voltage range from the pulses generated by the detector, a scaler for the pulses selected by the pulse height analyzer; and a counting time counter for measuring the elapsed time in pulse counting by the scaler. The X-ray fluorescence spectrometer furthermore includes a frequency divider for generating a read-out signal for each of the predetermined scanning intervals in the linkage means. In response to the read-out signal from the frequency devider, the scaler reads the count and the counting time counter reads the counting time. The X-ray fluorescence spectrometer also includes a correction calculating means to correct the counts based on the counting time.
In the X-ray fluorescence spectrometer according to the present invention, since the counting time counter and the frequency divider are used to determine the counting time for each of the predetermined scanning intervals, and the count for each scanning interval is corrected by the correction calculating means on the basis of the corresponding counting time, an accurate intensity of the fluorescent X-ray for each scanning interval including the drive in the ranges of accelerated and decelerated speed can be obtained where the linkage means is driven at a high speed. Accordingly, in the fluorescent X-ray analysis, the qualitative analysis as well as the semi-quantitative analysis can be rapidly and accurately performed over a relatively wide range of wavelength. In other words, the rapid and accurate analysis is possible with the continuous scan.
In order to accomplish the foregoing object, the present invention also provides an X-ray diffractometer which includes a sample support to place a sample to be analyzed; an X-ray source for irradiating the sample with incident X-rays; a detector to generate pulses having the voltage proportional to the energy of the diffracted X-rays in a number proportional to the X-ray intensity; and a linkage means for linking the drive of the sample support with the detector to allow continuous scan so as that the diffracted X-rays irradiate the detector.
The X-ray difractometer referred to above also includes a pulse height analyzer for selecting the pulses which fall within a predetermined voltage range from the pulses generated by the detector, a scaler for counting the pulses selected by the pulse height analyzer; and a counting time counter for measuring the elapsed time in pulse counting by the scaler. The X-ray diffractometer futhermore includes a frequency divider for generating a read-out signal for each of the predetermined scanning intervals in the linkage means. In response to the read-out signal from the frequency devider, the scaler reads the count and the counting time counter reads the counting time. The X-ray diffractometer also includes a correction calculating means to correct the counts based on the counting time.
In the X-ray diffractometer according to the present invention, since the counting time counter and the frequency divider are used to determine the counting time for each of the predetermined scanning intervals, and the count for each scanning interval is corrected by the correction calculating means on the basis of the corresponding counting time, an accurate intensity of the diffracted X-ray for each scanning interval can be obtained and, accordingly, the rapid and accurate analysis is possible with the continuous scan in the X-ray diffraction analysis.
In order to accomplish the previously described object, the present invention furthermore provides an X-ray fluorescence spectrometer which includes a measuring unit for irradiating with primary X-rays a band-shaped sample made up with multi-layer film and being transported in a direction lengthwise thereof, to excite the sample to emit a fluorescent X-ray and for generating pulses in a number proportional to an intensity of the fluorescent X-ray emitted from the sample; a drive means for shuttling the measuring unit in a direction widthwise of the sample that is perpendicular to the lengthwise direction of the sample; and a sample edge detecting means mounted on the measuring unit for detecting each edge of the sample in the widthwise direction thereof.
The X-ray fluorescence spectrometer also includes a pulse height analyzer for selecting the pulses which fall within a predetermined voltage range from the measuring unit; a scaler for counting the pulses selected by the pulse height analyzer; a counting time counter for measuring the elapsed time in pulse counting by the scaler; a frequency divider for generating a read-out signal for each fixed moving range in the drive means, stating from a position where the sample edge detecting means detects one of the edges of the sample in the widthwise direction thereof. In response to the read-out signal from the frequency devider, the scaler reads the count and the counting time counter reads the counting time. The X-ray diffractometer also includes a correction calculating means to correct the counts based on the counting time; and a coating weight calculating means for determining a coating weight or thickness of at least one of the layers in the multi-layers, for each fixed moving range, based on the count corrected by the correction calculating means.
In the X-ray fluorescence spectrometer, since the correction calculating means corrects the count of the pulses generated by the measuring unit, based on the counting time which is the time required for the measuring unit to move, for each moving range on the sample in the widthwise direction thereon the coating weight or thickness can be rapidly and accurately determined for each section of the sample without the discrepancy in correspondence to each section in the sample even if the moving speed varies in high moving speed by setting the length of moving range in the widthwise direction. Thus, during the fluorescent X-ray analysis, the rapid and accurate analysis is possible with the continuous scanning.
The X-ray fluorescence spectrometer can be satisfactorily worked out where the sample is a release coated paper on which silicone is coated and the coating weight of thickness of silicone coated layer is analyzed. Or a magnetic tape which a magnetic material is coated and the coating weight or thickness of the magnetic material layer is analyzed.
Any one of the X-ray analyzing apparatuses described above according to the present invention, the like means or the moving means may have a rotary encoder so that the frequency divider can generate the read-out signal based on a signal fed from the rotary encoder.